I've seen several SF&F question comments asking the poster if what they were asking about was really science fiction. Some were (but neededmore detail), some weren't, some were edge cases.
So, as an example, I'd like to ask about one of those edge cases, the original 1979 movie Mad Max.
Although the movie's Wikipedia article uses the word "dystopian", it seems to me this use is offhand and careless with nothing to support it. Nothing in that movie couldn't have happened in 1979.
This use of "dystopian" seems to be a retcon of sorts based on the sequels, whose post-apocalyptic aesthetic puts them squarely in the SF category.
Is MM really any different from other crime revenge fantasies of the time, such as Death Wish or Dirty Harry?
Update: There have been reponses that "there weren't motorcycle gangs roaming the desert at the time". Really? Motorcycle gangs roaming the desert randomly terrorizing civilians was certainly plausible for the time, and an expressions of fears about that particular moment.
Does an expression of people's fears about what was going on at the time necessarily make it "post-apocalyptic"? "The near future" can be a euphemism for "now".
(I accepted Valorum's answer because he showed a poster where the original movie was promoted as a projection into the future).